1. Field of the Invention
Our invention relates to the preparation of halogenated starch ethers and to water-insoluble, nitrogen-containing substitution products thereof which are useful as anionic, cationic, or chelating complexing agents.
2. Description of the Prior Art
Derivatized starches containing nitrogen functionalities have long been the subject of extensive investigation. Cationic tertiary and quaternary ammonium starch ethers have been utilized for floculating materials suspended in aqueous systems including anionic starches, celluloses, clays, ores, silt, coal, and the like. They have also found use in papermaking as filler and pigment retention aids, sizing agents, and strengthening agents.
The effectiveness of these agents is generally related to their solubility and the degree of substitution (D.S.) of the cationic functionality. These properties are determined to a large extent upon the procedure for etherification as well as the degree of gelatinization and crosslinking of the starch moiety prior to and during derivatization. One of the predominant etherification mechanisms as taught in Paschall, U.S. Pat. No. 2,876,217, involves reacting an amine with an epihalohydrin to form an intermediate reaction product, which can be etherified with granular starch under strongly alkaline conditions. Paschall teaches that unless precautions are taken, the starch will be crosslinked by residual epihalohydrin, resulting in an ungelatinizable product which is considered undesirable of his prospective uses. The highest D.S. taught by Paschall is 0.065. In U.S. Pat. No. 2,995,513, Paschall discloses products having higher D.S.'s and improved flocculating capacities obtained by gelatinizing prior to etherification.
In U.S. Pat. No. 3,243,426 and 3,422,087, Caesar prepares gelatinizable cationic starches by essentially the same route as Paschall. He additionally teaches that gelatinization during etherification can be avoided by conducting this step in the absence of an aqueous medium.
By a slightly different mechanism, Shildneck (U.S. Pat. No. 3,346,563) prepares cationic starches via an intermediate reaction product of an amine and an allyl halide. The reactant starch may be either granular or gelatinized, and the conditions of his process are selected to minimize crosslinking. In an improvement over Shildneck et al., Moser et al., U.S. Pat. No. 3,842,005, teaches that gelatinized, noncrosslinked quaternary ammonium starch ethers having D.S. as high as 1.07 can be prepared by employing allyl quaternary ammonium halides which are essentially free from excess allyl halide and allyl alcohol.
In the preparation of a cation exchange starch, Bullock et al. (U.S. Pat. No. 3,065,222) prepares a water-insoluble granular product by crosslinking the starch prior to reacting it with either monochloroacetic acid or 2-chlorotriethylamine.
There are many applications for nitrogen-containing starch ethers, such as in the flocculation and removal of anions from wastewaters, which require that the product be insoluble (i.e., ungelatinizable) in aqueous solutions and simultaneously have a high D.S. It would also be desirable to prepare starch ethers having chelating or anionic reactant groups for the removal of heavy metals and other cations from solution. The etherification procedures heretofore known in the prior art as discussed above preclude the formation of many of these products.